package com.idenger.modules.edu.web.utils;

import org.springframework.web.servlet.view.AbstractView;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;

/**
 * Created by mugy on 2017/7/11.
 */
public class ByteRangeViewRender{

    private static final int DEFAULT_BUFFER_SIZE = 20480; // ..bytes = 20KB.
    private static final long DEFAULT_EXPIRE_TIME = 604800000L; // ..ms = 1 week.
    private static final String MULTIPART_BOUNDARY = "MULTIPART_BYTERANGES";

    public void renderMergedOutputModel(File file,String contentType, HttpServletRequest request, HttpServletResponse response)
            throws Exception {
        if (file == null || !file.exists()) {
            response.sendError(HttpServletResponse.SC_NOT_FOUND);
            return;
        }
        String fileName = file.getName();
        long length = file.length();
        long lastModified = file.lastModified();
        String eTag = fileName + "_" + length + "_" + lastModified;
        long expires = System.currentTimeMillis() + DEFAULT_EXPIRE_TIME;

        // Validate request headers for caching ---------------------------------------------------

        // If-None-Match header should contain "*" or ETag. If so, then return 304.
        String ifNoneMatch = request.getHeader("If-None-Match");
        if (ifNoneMatch != null && matches(ifNoneMatch, fileName)) {
            response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            response.setHeader("ETag", eTag); // Required in 304.
            response.setDateHeader("Expires", expires); // Postpone cache with 1 week.
            return;
        }

        // If-Modified-Since header should be greater than LastModified. If so, then return 304.
        // This header is ignored if any If-None-Match header is specified.
        long ifModifiedSince = request.getDateHeader("If-Modified-Since");
        if (ifNoneMatch == null && ifModifiedSince != -1 && ifModifiedSince + 1000 > lastModified) {
            response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            response.setHeader("ETag", eTag); // Required in 304.
            response.setDateHeader("Expires", expires); // Postpone cache with 1 week.
            return;
        }

        // Validate request headers for resume ----------------------------------------------------

        // If-Match header should contain "*" or ETag. If not, then return 412.
        String ifMatch = request.getHeader("If-Match");
        if (ifMatch != null && !matches(ifMatch, fileName)) {
            response.sendError(HttpServletResponse.SC_PRECONDITION_FAILED);
            return;
        }

        // If-Unmodified-Since header should be greater than LastModified. If not, then return 412.
        long ifUnmodifiedSince = request.getDateHeader("If-Unmodified-Since");
        if (ifUnmodifiedSince != -1 && ifUnmodifiedSince + 1000 <= lastModified) {
            response.sendError(HttpServletResponse.SC_PRECONDITION_FAILED);
            return;
        }

        // Validate and process range -------------------------------------------------------------

        // Prepare some variables. The full Range represents the complete file.
        Range full = new Range(0, length - 1, length);
        List<Range> ranges = new ArrayList<>();

        // Validate and process Range and If-Range headers.
        String range = request.getHeader("Range");
        if (range != null) {

            // Range header should match format "bytes=n-n,n-n,n-n...". If not, then return 416.
            if (!range.matches("^bytes=\\d*-\\d*(,\\d*-\\d*)*$")) {
                response.setHeader("Content-Range", "bytes */" + length); // Required in 416.
                response.sendError(HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE);
                return;
            }

            String ifRange = request.getHeader("If-Range");
            if (ifRange != null && !ifRange.equals(eTag)) {
                try {
                    long ifRangeTime = request.getDateHeader("If-Range"); // Throws IAE if invalid.
                    if (ifRangeTime != -1 && ifRangeTime + 1000 < lastModified) {
                        ranges.add(full);
                    }
                } catch (IllegalArgumentException ignore) {
                    ranges.add(full);
                }
            }

            // If any valid If-Range header, then process each part of byte range.
            if (ranges.isEmpty()) {
                for (String part : range.substring(6).split(",")) {
                    // Assuming a file with length of 100, the following examples returns bytes at:
                    // 50-80 (50 to 80), 40- (40 to length=100), -20 (length-20=80 to length=100).
                    long start = sublong(part, 0, part.indexOf("-"));
                    long end = sublong(part, part.indexOf("-") + 1, part.length());

                    if (start == -1) {
                        start = length - end;
                        end = length - 1;
                    } else if (end == -1 || end > length - 1) {
                        end = length - 1;
                    }

                    // Check if Range is syntactically valid. If not, then return 416.
                    if (start > end) {
                        response.setHeader("Content-Range", "bytes */" + length); // Required in 416.
                        response.sendError(HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE);
                        return;
                    }

                    // Add range.
                    ranges.add(new Range(start, end, length));
                }
            }
        }

        // Prepare and initialize response --------------------------------------------------------

        // Get content type by file name and set content disposition.
        String disposition = "inline";

        // If content type is unknown, then set the default value.
        // For all content types, see: http://www.w3schools.com/media/media_mimeref.asp
        // To add new content types, add new mime-mapping entry in web.xml.
        if (contentType == null) {
            contentType = "application/octet-stream";
        } else if (!contentType.startsWith("image")) {
            // Else, expect for images, determine content disposition. If content type is supported by
            // the browser, then set to inline, else attachment which will pop a 'save as' dialogue.
            String accept = request.getHeader("Accept");
            disposition = accept != null && accepts(accept, contentType) ? "inline" : "attachment";
        }

        // Initialize response.
        response.reset();
        response.setBufferSize(DEFAULT_BUFFER_SIZE);
        response.setHeader("Content-Disposition", disposition + ";filename=\"" + fileName + "\"");
        response.setHeader("Accept-Ranges", "bytes");
        response.setHeader("ETag", eTag);
        response.setDateHeader("Last-Modified", lastModified);
        response.setDateHeader("Expires", expires);

        // Send requested file (part(s)) to client ------------------------------------------------

        // Prepare streams.
        RandomAccessFile input = null;
        OutputStream output = null;

        try {
            // Open streams.
            input = new RandomAccessFile(file, "r");
            output = response.getOutputStream();

            if (ranges.isEmpty() || ranges.get(0) == full) {

                // Return full file.
                Range r = full;
                response.setContentType(contentType);
                response.setHeader("Content-Range", "bytes " + r.start + "-" + r.end + "/" + r.total);
                response.setHeader("Content-Length", String.valueOf(r.length));

                copy(input, output, r.start, r.length);

            } else if (ranges.size() == 1) {

                // Return single part of file.
                Range r = ranges.get(0);
                response.setContentType(contentType);
                response.setHeader("Content-Range", "bytes " + r.start + "-" + r.end + "/" + r.total);
                response.setHeader("Content-Length", String.valueOf(r.length));
                response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT); // 206.

                // Copy single part range.
                copy(input, output, r.start, r.length);

            } else {

                // Return multiple parts of file.
                response.setContentType("multipart/byteranges; boundary=" + MULTIPART_BOUNDARY);
                response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT); // 206.

                // Cast back to ServletOutputStream to get the easy println methods.
                ServletOutputStream sos = (ServletOutputStream) output;

                // Copy multi part range.
                for (Range r : ranges) {
                    // Add multipart boundary and header fields for every range.
                    sos.println();
                    sos.println("--" + MULTIPART_BOUNDARY);
                    sos.println("Content-Type: " + contentType);
                    sos.println("Content-Range: bytes " + r.start + "-" + r.end + "/" + r.total);

                    // Copy single part range of multi part range.
                    copy(input, output, r.start, r.length);
                }

                // End with multipart boundary.
                sos.println();
                sos.println("--" + MULTIPART_BOUNDARY + "--");
            }
        } finally {
            close(output);
            close(input);
        }

    }

    // Helpers (can be refactored to public utility class) ----------------------------------------

    private void close(Closeable resource) {
        if (resource != null) {
            try {
                resource.close();
            } catch (IOException ignore) {
            }
        }
    }

    private void copy(RandomAccessFile input, OutputStream output, long start, long length) throws IOException {
        byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
        int read;

        try {
            if (input.length() == length) {
                // Write full range.
                while ((read = input.read(buffer)) > 0) {
                    output.write(buffer, 0, read);
                }
            } else {
                input.seek(start);
                long toRead = length;

                while ((read = input.read(buffer)) > 0) {
                    if ((toRead -= read) > 0) {
                        output.write(buffer, 0, read);
                    } else {
                        output.write(buffer, 0, (int) toRead + read);
                        break;
                    }
                }
            }
        } catch (IOException ignore) {
        }
    }

    private long sublong(String value, int beginIndex, int endIndex) {
        String substring = value.substring(beginIndex, endIndex);
        return (substring.length() > 0) ? Long.parseLong(substring) : -1;
    }

    private boolean accepts(String acceptHeader, String toAccept) {
        String[] acceptValues = acceptHeader.split("\\s*(,|;)\\s*");
        Arrays.sort(acceptValues);
        return Arrays.binarySearch(acceptValues, toAccept) > -1
                || Arrays.binarySearch(acceptValues, toAccept.replaceAll("/.*$", "/*")) > -1
                || Arrays.binarySearch(acceptValues, "*/*") > -1;
    }

    private boolean matches(String matchHeader, String toMatch) {
        String[] matchValues = matchHeader.split("\\s*,\\s*");
        Arrays.sort(matchValues);
        return Arrays.binarySearch(matchValues, toMatch) > -1
                || Arrays.binarySearch(matchValues, "*") > -1;
    }

    // Inner classes ------------------------------------------------------------------------------

    protected class Range {
        long start;
        long end;
        long length;
        long total;

        public Range(long start, long end, long total) {
            this.start = start;
            this.end = end;
            this.length = end - start + 1;
            this.total = total;
        }
    }
}
